Japanese Patent Laid-open Publication No. 2000-320502 discloses related art of a control valve body of an automatic transmission. According to this related art, a valve body member which has a hydraulic oil channel groove formed on at least one surface thereof and constituting a hydraulic circuit, and a cap member which is attached to the surface of the valve body member where the channel groove is formed and covers the channel groove, are provided. On the cap member, a supporting portion is formed, which has a side surface for supporting the partition between the channel grooves on the valve body member, against pressing pressure applied from an oil channel in the form of the channel groove. With this arrangement, the thickness of the partition formed on the valve body member, and accordingly the size and weight of the valve body member, can be reduced.
In addition to the above, Japanese Patent Laid-open Publication No. Hei 10-238628 discloses a control valve body of an automatic transmission. Further, as other background art, Japanese Patent No. 3286224 and Japanese Patent Laid-open Publication No. Hei 11-124692 disclose a magnesium-molded product.
A control valve body of an automatic transmission is generally manufactured through aluminum die-casting. A hydraulic oil channel groove defined on the valve body is formed using a steel casting mold. However, in an attempt to reduce the width of the channel groove in manufacturing the valve body through aluminum die-casting, the casting mold in use is readily deteriorated due to the reaction between the aluminum melted liquid and the steel casting mold and heat exhaustion or the like in a cooling and heating cycle. Therefore, it is not practicable to employ a valve body having a channel groove of a narrower width.
According to Japanese Patent Laid-open Publication No. 2000-320502, where size and weight reduction of the valve body is attempted by forming a thinner partition, a problem remains that sufficient size and weight reduction of the valve body cannot be readily achieved as employment of a channel groove having a narrower width is not practicable due to the above-described reason.
The present invention aims to provide a control valve body of an automatic transmission in which a hydraulic oil channel groove having a narrower width can be formed, and a method for manufacturing such a control valve body.